The Linux Programming Interface

466 Chapter 22

z Loop until gotSigquit is set r. Each loop iteration performs the following steps:

• Display the current value of the signal mask using our printSigMask() function.


• Simulate a critical section by executing a CPU busy loop for a few seconds.


• Display the mask of pending signals using our printPendingSigs() function
  (Listing 20-4).


• Uses sigsuspend() to unblock SIGINT and SIGQUIT and wait for a signal (if one
  is not already pending).
  z Use sigprocmask() to restore the process signal mask to its original state t, and
  then display the signal mask using printSigMask() y.

Listing 22-5: Using sigsuspend()

–––––––––––––––––––––––––––––––––––––––––––––––––––– signals/t_sigsuspend.c

#define _GNU_SOURCE /* Get strsignal() declaration from <string.h> */

#include <string.h>

#include <signal.h>

#include <time.h>

#include "signal_functions.h" /* Declarations of printSigMask()

and printPendingSigs() */

#include "tlpi_hdr.h"

static volatile sig_atomic_t gotSigquit = 0;

static void

handler(int sig)

{

printf("Caught signal %d (%s)\n", sig, strsignal(sig));

/* UNSAFE (see Section 21.1.2) */

if (sig == SIGQUIT)

gotSigquit = 1;

}

int

main(int argc, char *argv[])

{

int loopNum;

time_t startTime;

sigset_t origMask, blockMask;

struct sigaction sa;

q printSigMask(stdout, "Initial signal mask is:\n");

sigemptyset(&blockMask);

sigaddset(&blockMask, SIGINT);

sigaddset(&blockMask, SIGQUIT);

w if (sigprocmask(SIG_BLOCK, &blockMask, &origMask) == -1)

errExit("sigprocmask - SIG_BLOCK");

sigemptyset(&sa.sa_mask);

sa.sa_flags = 0;

sa.sa_handler = handler;